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Marvin Xiang Ce Seow, Yushi Morioka, and Tomoki Tozuka

Abstract

Influences from the tropical Pacific and Indian Oceans, and atmospheric internal variability on the South China Sea (SCS) atmospheric circulation and cold tongue (CT) variability in boreal winter and the relative roles of remote forcings at interannual time scales are studied using observational data, reanalysis products, and coupled model experiments. In the observation, strong CT years are accompanied by local cyclonic wind anomalies, which are an equatorial Rossby wave response to enhanced convection over the warmer-than-normal western equatorial Pacific associated with La Niña. Also, the cyclonic wind anomalies are an atmospheric Kelvin wave response to diabatic cooling anomalies linked to both the decaying late fall negative Indian Ocean Dipole (IOD) and winter atmospheric internal variability. Partially coupled experiments reveal that both the tropical Pacific air-sea coupling and atmospheric internal variability positively contribute to the coupled variability of the SCS CT, while the air-sea coupling over the tropical Indian Ocean weakens such variabilities. The northwest Pacific anticyclonic wind anomalies that usually precede El Niño–Southern Oscillation-independent negative IOD generated under the tropical Indian Ocean air-sea coupling undermine such variabilities.

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Beata Latos, Thierry Lefort, Maria K. Flatau, Piotr J. Flatau, Donaldi S. Permana, Dariusz B. Baranowski, Jaka A.I. Paski, Erwin Makmur, Eko Sulystyo, Philippe Peyrillé, Zhe Feng, Adrian J. Matthews, and Jerome M. Schmidt

Abstract

On the basis of detailed analysis of a case study and long-term climatology, it is shown that equatorial waves and their interactions serve as precursors for extreme rain and flood events in the central Maritime Continent region of southwest Sulawesi, Indonesia. Meteorological conditions on January 22, 2019 leading to heavy rainfall and devastating flooding in this area are studied. It is shown that a convectively coupled Kelvin wave (CCKW) and a convectively coupled equatorial Rossby wave (CCERW) embedded within the larger-scale envelope of the Madden-Julian Oscillation (MJO) enhanced convective phase, contributed to the onset of a mesoscale convective system which developed over the Java Sea. Low-level convergence from the CCKW forced mesoscale convective organization and orographic ascent of moist air over the slopes of southwest Sulawesi. Climatological analysis shows that 92% of December-January-February floods and 76% of extreme rain events in this region were immediately preceded by positive low-level westerly wind anomalies. It is estimated that both CCKWs and CCERWs propagating over Sulawesi double the chance of floods and extreme rain event development, while the probability of such hazardous events occurring during their combined activity is eight times greater than on a random day. While the MJO is a key component shaping tropical atmospheric variability, it is shown that its usefulness as a single factor for extreme weather-driven hazard prediction is limited.

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Arun Kumar, Jieshun Zhu, and Wanqiu Wang

also extend northeast into the extratropical Pacific oceans. The large explained variance might be due to atmospheric Rossby wave activity associated with the MJO-related convections. Over the land, except for the tropical Africa there are also local regions of larger variance explained in the middle Eurasian continent, Arabian Peninsula, part of Australia and western coastal and northeastern regions of the south American continent. For the north American continent, relatively larger value of

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Kevin E. Trenberth and Yongxin Zhang

Zealand downstream. Hence the change in local winds also force some modifications in surface fluxes and wind stress. Any link between ENSO-related variations in the ITF and the Tasman Sea heat waves has been generally assigned to the atmospheric bridge connections. The studies thus far have overlooked the likelihood that there is also a direct ocean connection through the changes in mass and heat transport with the ITF that indeed relate to opposite changes in the East Australian Current region

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Wan-Ling Tseng, Huang-Hsiung Hsu, Noel Keenlyside, Chiung-Wen June Chang, Ben-Jei Tsuang, Chia-Ying Tu, and Li-Chiang Jiang

1. Introduction The warm pool in the tropical western Pacific, including the Maritime Continent (MC), is one of the most convective regions on Earth. It contributes substantial energy to drive the atmospheric general circulation and global climate system. Within the warm pool, the MC plays a critical role in influencing the fluctuations in global atmospheric energy and hydrological cycles by inducing tropical heating and exciting poleward-emanating Rossby waves ( Neale and Slingo 2003 ). The

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James H. Ruppert Jr., Xingchao Chen, and Fuqing Zhang

through two concurrent mechanisms, the diurnal change in atmospheric radiative heating conspires to favor nocturnal organized deep convection ( Gray and Jacobson 1977 ; Randall et al. 1991 ; Ruppert and Hohenegger 2018 ). While this argument has primarily been invoked to explain nocturnal–early morning rainfall over oceans ( Yang and Slingo 2001 ; Yang and Smith 2006 ), its potential role over land has also been implicated ( Zhang et al. 2018 ). A striking commonality between both the coastal and

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Wei-Ting Chen, Shih-Pei Hsu, Yuan-Huai Tsai, and Chung-Hsiung Sui

-real-time observations. Climatology data are used to produce anomalies on interannual time scales and to filter out tropical waves. Near-real-time data are processed for monitoring weather events. a. Observation and reanalysis datasets For the climatological outgoing longwave radiation (OLR) field, we use interpolated data obtained from National Oceanic and Atmospheric Administration (NOAA) polar-orbiting satellite ( Liebmann and Smith 1996 ). It has daily 2.5° × 2.5° resolution and the period between January 1979

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James H. Ruppert Jr. and Fuqing Zhang

northwestern South America. Part II: Model simulations . Mon. Wea. Rev. , 131 , 813 – 829 , https://doi.org/10.1175/1520-0493(2003)131<0813:DPORIN>2.0.CO;2 . 10.1175/1520-0493(2003)131<0813:DPORIN>2.0.CO;2 Wheeler , M. , and H. Nguyen , 2015 : Equatorial waves. Encyclopedia of Atmospheric Sciences , 2nd ed. J. Pyle and F. Zhang, Eds., Vol. 6, Elsevier, 102–112, https://doi.org/10.1016/B978-0-12-382225-3.00414-X . 10.1016/B978-0-12-382225-3.00414-X Yamanaka , M. D. , S.-Y. Ogino , P.-M. Wu

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Yan Zhu, Tim Li, Ming Zhao, and Tomoe Nasuno

; Khouider et al. 2012 ) prescribed the tilting of atmospheric waves or synoptic perturbations that are embedded within the MJO in such a way that it favors MJO growth through eddy vertical momentum transport. But such a tilting structure and preferred location for distinctive low-frequency and high-frequency waves require further observational validation. While focusing on boreal summer ISO, Hsu and Li (2011) diagnosed the observational data in the western North Pacific and found that vertical eddy

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Lei Song and Renguang Wu

of the East Asian trough. The southeastward flow to the rear of the East Asian trough favors the southward intrusion of cold air, leading to the invasion of cold events to eastern China ( Zhang et al. 1997 ; Jeong and Ho 2005 ; Takaya and Nakamura 2005a , b ; Bueh et al. 2011 ; Song et al. 2016 ; Song and Wu 2017 ). The development of the Siberian high and the East Asian trough is closely related to the Rossby wave trains propagating along the polar front jet and the subtropical jet

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